Add a config object

- add the following file:
  + src/urban_meal_delivery/_config.py
- a config module is created holding two sets of configurations:
  + production => against the real database
  + testing => against a database with test data
- the module is "protected" (i.e., underscore) and imported at the
  top level via a proxy-like object `config` that detects in which of
  the two environments the package is being run

src/urban_meal_delivery/__init__.py

@@ -6,8 +6,11 @@ Example:
     True
 """
 
+import os as _os
 from importlib import metadata as _metadata
 
+from urban_meal_delivery import _config  # noqa:WPS450
+
 
 try:
     _pkg_info = _metadata.metadata(__name__)
@@ -21,3 +24,7 @@ else:
     __author__ = _pkg_info['author']
     __pkg_name__ = _pkg_info['name']
     __version__ = _pkg_info['version']
+
+
+# Little Hack: "Overwrites" the config module so that the environment is already set.
+config = _config.get_config('testing' if _os.getenv('TESTING') else 'production')